Merge branch 'release-21.8.0' into master

[lib] Bump version: 21.8.0rc1 → 21.8.0

[exec] Bump version: 21.8.0rc1 → 21.8.0

[core] Bump version: 21.8.0rc1 → 21.8.0

[cli] Bump version: 21.8.0rc1 → 21.8.0

[lib] Bump version: 21.7.0.dev3 → 21.8.0rc1

[exec] Bump version: 21.7.0.dev3 → 21.8.0rc1

[core] Bump version: 21.7.0.dev3 → 21.8.0rc1

[cli] Bump version: 21.7.0.dev3 → 21.8.0rc1

[lib] Bump version: 21.7.0.dev2 → 21.7.0.dev3